1. Field of the Invention
The present invention relates to a method and apparatus for modifying the gaseous atmosphere in a sealed receptacle containing a deteriorative material or a material of which controlled fluid exposure is desired. In a preferred embodiment, the present invention is directed to a method and apparatus for extracting, modifying, or exchanging the gases within a closed, sealed receptacle, while inhibiting the structural collapse of the receptacle. The invention is especially concerned with treating foods in the original flexible packages in which the foods are initially wrapped for purposes of transport, display and marketing.
2. Description of the Prior Art
The shelf life of many food products at both a refrigerated state and at room temperature can be greatly extended if the food product is placed in a substantially oxygen free environment. One way of achieving this oxygen free environment is to evacuate a package containing the food product to a very high level of vacuum. However, when flexible packaging is involved, as is often the case in consumer ready packaging, the use of a high vacuum can distort, compact and crush the enclosed product as the vacuum is applied. For example, bakery products can readily be squeezed or compressed so that they lose their consumer appeal. Shredded cheeses can be compacted to such an extent that they require reshredding. Fruit products can be bruised with a resultant loss of both appearance and flavor.
Meat, fruit and vegetable products subjected to vacuum packing can also undergo liquid purge which diminishes their appearance and flavor. Additionally, meat products subjected to vacuum packaging often adopt a purplish color since no oxymyoglobin is formed due to the lack of oxygen. This color is sometimes unacceptable for domestic retail marketing, and hence the product must be removed from the vacuum package prior to display and repackaged in a way so as to allow the characteristic red "bloom" to appear in the meat product.
To overcome the aforedescribed disadvantages, gas packaging has been used as an alternative to vacuum packing. Gas packaging entails a modification of the atmosphere within the receptacle housing the product so as to introduce a growth inhibiting agent, i.e. an inert gas, or an oxygenating agent, into the receptacle. As disclosed in applicant's copending application Ser. No. 214,195, it may also be desirable to modify the gas within the receptacle to include a desired concentrations of an oxidizing agent, e.g. ozone, so as to reduce or eliminate bacterial concentration within the receptacle.
In instances where gas flush packaging is utilized, it is often desirable to remove a substantial portion of the original, resident atmosphere within the receptacle before introducing a second gas or combination of gases. This is desirable so as to decrease the amount of the secondary gas necessary to beneficially affect the containerized product. If evacuation or partial evacuation of the receptacle is not first undertaken, the secondary gas will be diluted and will therefore be required in greater quantities or concentrations in order to achieve its intended purpose. At least partial gas extraction is therefore desirable in order to remove the resident gas preliminary to the introduction of a second gas. This gas extraction, however, if conducted in a conventional manner, will also bring about the disadvantages noted above in connection with vacuum packaging in that the package will undergo distortion or collapse.
A variety of devices have been developed to address the problems associated with the collapse of a flexible container or receptacle during gas exchange or extraction. One such device is seen in U.S. Pat. No. 1,591,932 (the '932 patent) as issued to Young. The '932 patent discloses a method and apparatus for replacing air in a filled container with an inert gas. In the '932 patent, the receptacle is placed within a vacuum chamber and the pressures inside and outside the receptacle regulated so as to avoid the deformation or collapse of the walls of the receptacle. Gas exchange in the '932 patent is accomplished by withdrawing the resident atmosphere from the receptacle via a vent hole while maintaining an equal pressure within the vacuum chamber. When the addition of the inert gas is desired, pressure equalization is accomplished via a yoke which is activated by the pressure of the gas injected into the receptacle.
Disadvantages of the apparatus disclosed in the '932 patent include the need to form an aperture in the container in order to achieve evacuation and repressurization in addition to the need to utilize a secondary sealing step to maintain the second atmosphere within the receptacle. As a result, the solution proposed by Young is not commercially feasible.